1. Field of the Invention
The present invention relates to a wireless packet communication system and a base station. More particularly, the present invention relates to a packet wireless communication system and a base station having an adjusting function which adjusts flexibly the throughput difference between mobile units; and a control function which performs the control according to the priority between mobile units.
2. Description of Related Art
In a wireless packet communication system called High Data Rate (hereinafter, referred to as HDR) system, a scheduler is defined for determining a down link transmission timing. A base station in a conventional HDR system, periodically computes a value of an evaluation function Fi (n) for each mobile unit “i” under the base station, and downlink transmission is carried out for a mobile unit showing maximum value of Fi (n) (a transmission timing is assigned). When downlink transmission is carried out, the value of the evaluation function Fi (n) temporarily decreases, and increases again. That is, the value of the evaluation function Fi (n) reciprocates alternately between a maximum value and a minimum value. When the value is around maximum, downlink transmission is carried out. In Proportional Fairness algorithm proposed by “Processing of IEEE VTC-2000 Spring, “Data Throughput of CDMA-HDR a High Efficiency-High Data Rate Personal Communication Wireless System”, A. Jalali, R. Padovani, R. Pankaj”, the evaluation function Fi (n) at a time “n” of a mobile unit “i” is expressed by the following formula (2).                                           F            i                    ⁡                      (            n            )                          =                                            DRC              i                        ⁡                          (              n              )                                                          R              i                        ⁡                          (              n              )                                                          (        2        )                                                      R            i                    ⁡                      (            n            )                          =                                            (                              1                -                                  1                                      t                    c                                                              )                        ×                                          R                i                            ⁡                              (                                  n                  -                  1                                )                                              +                                    1                              t                c                                      ×                                          r                i                            ⁡                              (                                  n                  -                  1                                )                                                                        (        7        )            
wherein DRCi (n) represents a required rate in a slot “n” of a mobile unit “i”;
ri (n) represents a transmission rate in a slot “n” relevant to a mobile unit “i”;
Ri (n) represents an average transmission rate in a slot “n” relevant to a mobile unit “i” or an indicator in analogous to the average transmission rate;
tc represents a time constant.
Formula (7) is a formula for obtaining an exponential weighting average immediately close to the transmission rate assigned to the mobile unit “i”.
According to a conventional Proportional Fairness algorithm, control performs such that throughput for each mobile unit is simply proportional to the required rate from the mobile unit. Therefore, according to the conventional Proportional Fairness algorithm, a difference in required rate between mobile units appears as a throughput difference as it is, disabling flexible adjustment of a throughput difference between mobile units. In addition, control according to the priority between mobile units is impossible as well.
However, in order to apply the Proportional Fairness algorithm to operation of a communication system in actuality, the following features are required:
a function for adjusting a throughput difference between mobile units; and
a function for controlling a throughput difference for each class by classifying the mobile units.
The present invention provides a wireless packet communication system and a base station having capability to enable actual flexible operation by adding these function to the Proportional Fairness algorithm.